Cutting Insert

ABSTRACT

The invention relates to a cutting insert for clamping into a disc-type or strip-shaped tool body, in particular, for milling crankshafts, whereby said insert is substantially cuboid-shaped and has two front faces, the distance between which defines the width ( 4 ) of the cutting insert, two side faces, serving as cutting faces ( 6 ) and the distance between which determines the thickness ( 3 ) of the cutting insert as well as an upper and a lower side face ( 5 ), whereby a convex face ( 1 ) is arranged between the front faces and the upper and lower side faces, so that the upper and lower side faces and the convex face form cutting edges ( 7 ) each with a side face, which terminate laterally in cutting corners. According to said invention, the cutting insert is characterised in that an inwardly-tapered face ( 2 ) adjoins the convex face, which allows the cutting edge to protrude, tapered chamfers ( 13, 14 ) are provided between the inwardly-tapered faces ( 2 ) of the front face on both sides of a planar supporting surface to the outer edge and the width and the thickness of the cutting insert vary from each other by a maximum of 20% and preferably have identical lengths.

The invention relates to a cutting insert for clamping on a tool bodyshaped as a disk or bar, in particular for milling crankshafts, which issubstantially parallelepipedal and has two front faces whose spacingdefines the width of the cutting insert, two side faces that act ascutting surfaces and whose spacing determines the thickness of thecutting insert, and one upper and one lower end face, whereby one convexedge surface is arranged between each of the front faces and the upperend face and lower end face, such that the upper and lower end faces andthe convex edge surfaces each form with a side face a cutting edge (7)that terminates laterally in cutting corners. Such cutting inserts areknown for instance from DE 197 04 931 C1.

When machining the journal of a crankshaft, in order to be able to cut a900 corner, this journal must first be machined with a first cuttingplate before the cylinder surface is then machined by means of aso-called diameter plate. Productivity is relatively low if twodifferent indexable inserts, each with four cutting edges, are used forthese machining processes.

DE 197 04 931 C1 describes a cutting insert having a largelyparallelepipedal base body that is fitted as an indexable insert witheight usable cutting plates. This cutting insert has two planes arrangedparallel to one another and larger surfaces through which pass afastening hole and four side faces adjacent thereto, specifically twosmall end faces that are parallel to one another and larger longitudinalfaces that each have, in the center approximately along theirlongitudinal axis, a projecting bar that acts as a support surface whenclamping the cutting insert into a tool holder. The larger surfacesmerge via a rounded edge into smaller edge surfaces so that on thelongitudinal side approximately quarter circle-shaped cutting edgesresult as limit lines to the edge surfaces in the corner area. The longcutting edges as limit lines as [sic] between the larger surfaces andeach adjacent longitudinal surface are arcuately curved so that a bodyresults that is mirror-symmetrical to the longitudinal center plane andto the transverse center plane. With each of their ends and the roundededge, the long cutting edges form an angle between 70° and 80° betweenthe small edge surface and the larger surface. Despite these eightcutting edges, it is not possible to cut 90° corners with such a cuttinginsert because the secondary cutting edges would re-cut the cheeks ofthe 90° corner. Thus the use of these cutting plates is also limited tothe use of four cutting edges.

It is the object of the present invention to create an indexable insertfor machining a 90° corner that is suitable for performing all of thecutting operations required therefor, and that simultaneously has thegreatest possible number of effective cutting edges.

This object is attained using the cutting insert in accordance withclaim 1. In accordance with the invention, with this cutting insert aninwardly angled surface adjoins the convex edge surface, allowing thecutting corner to project. Furthermore, bevel faces angled to the outeredge are provided between the inwardly angled surfaces on the front faceon both sides of a planar support surface. The width and the thicknessof the cutting insert vary from each other by no more than 20%, and theypreferably are identical in length. What is attained using theabove-described measures is that the secondary cutting edges of theinventive cutting inserts are exposed so that they cannot re-cut a cheekof a crankshaft. Since because its thickness is approximately the sameas its depth the defined cutting insert can be used both for machining a90° corner and also for machining the outer pin diameter of acrankshaft, the inventive cutting insert replaces the two types ofindexable inserts normally used. This minimizes both the tool inventorycosts and the manufacturing costs for the cutting inserts and due to thegreater number of usable cuts leads to lower production costs.Additional embodiments of the invention are described in the subordinateclaims.

Thus in accordance with one further development of the invention themounting bolt that in the clamped condition passes through a bore thatis perpendicular to the front faces should be shorter than the cuttingedge length. This measure prevents excessive elongation of the mountingbolt.

Between the two above-described chamfers the front face preferably has aflat support surface, the support surfaces of the two spaced-apart frontfaces being exactly parallel to one another.

In one specific embodiment of the present invention, the slopes of theangled surfaces are 1° to 10° relative to the respective supportsurface, preferably 5°. The slope of the bevel faces to the planes ofthe respective support surface is between 15° and 30°, preferably 25°.

In order to create a secure support, the support surfaces are madeplanar on the respective front faces and flank the bore for receivingthe mounting bolt. The support surfaces and the lines that lie on theconvex edge surfaces and project therefrom extend coplanar with theplane of the support faces.

The cutting angle along the cutting edge is preferably selected to bepositive and is up to 20°, in particular 10° to 15°. For stabilizing thecutting edge, a chamfer that is preferably set at a chamfer angle of 0°to −15° can also be provided along the cutting edge. In accordance withone embodiment of the invention, the radius of curvature for the convexedge surfaces is between 1 mm and 1.5 mm, and is preferably 1.2 mm.

Additional embodiments and advantages of the cutting insert result fromthe drawings.

FIGS. 1 and 2 show different views of a first embodiment of an inventivecutting insert;

FIG. 3 is a top view onto the front face of another embodiment of thecutting insert;

FIG. 4 is a top view onto a side face of the cutting insert inaccordance with FIG. 3;

FIG. 5 is a detail B in accordance with FIG. 4; and

FIG. 6 is a sectional depiction E-E in accordance with FIG. 4.

The parallelepipedal cutting insert has opposite front faces 10 and 11that merge at the top and bottom via convex edge surfaces 1 into oneupper and lower end faces 5. The cutting surfaces are formed by sidefaces 6 that connect the front faces 10 and 11 to one another. Theseside faces 6 are bounded by cutting edges 7 formed by the upper andlower surfaces 5 and the convex edge surfaces 1 that extend over anangle of 90° in the corner area 7′ and have an inwardly inclinedsecondary cutting edge that is formed by an angled surface 2 connectedto the edge surface 1. This surface 2 extends across the entire width 3of the cutting insert and causes the secondary cutting edge to beexposed so that this secondary cutting edge cannot re-cut when thecutting tool is dipped into the workpiece at a right angle. The twofront faces 10 and 11 furthermore each have two planar support surfaces8 that are parallel to each other. A fastening hole 9 in which amounting bolt 12 is received is formed in the support surfaces. Bevelfaces 13 and 14 are provided on both sides of the flat support surfaces8 and between the angled surfaces 2 (above and below). A width 4 and athickness 3 of this cutting insert are nearly identical. The mountingbolt 12 should be no longer than the straight-line part of the cuttingedge 7 in order to prevent excess elongation of the bolt. The cuttinginsert is installed in the tool holder such that it engaged theworkpiece at an angle of exactly 90° and cuts a corner that is exactly90°. The cutting insert can preferably be employed for crankshaftmachining anywhere that the oil bond is so high that the opposingcutting edge does not also cut or is not exposed.

In another embodiment of the invention in accordance with FIGS. 3 and 4,identical parts are provided with the same reference numbers as for thecutting insert in accordance with FIGS. 1 and 2. The cutting insertshown in FIGS. 3 through 6 is also largely parallelepipedal, the width 4of the cutting insert seen in FIG. 4, which is largely determined by thedistance between the cutting edge corners 7′, being about 20% greaterthan the thickness 3 of the cutting insert. Adjacent each end of thefastening hole 9, above and below, are two small support surfaces 8 thatare somewhat trapezoidal as shown in FIG. 3 that are coplanar as shownby lines 15 in FIG. 4. As can be seen from FIG. 4, the line 15, whichapproximately forms the transition of the angled surface 2 to the curvedsurface 1, forms with the surfaces 8 a secure support in a single plane.As can be seen from FIG. 5, the angle α by which the secondary cuttingedge 17 is inwardly inclined relative to a vertical to the cutting edge7 is 5°. A chamfer 18 extends along the cutting edge at an angle β of(−)15° (see FIG. 6). The cutting angle γ is 12° to 15°.

The surfaces 16 can be provided with chip-shaping elements, the knownshapes according to the prior art, in the form of elevations ordepressions, being used. The chip-shaping elements should in particularserve for removing the chip and for chip breaking.

The inventive cutting insert can comprise a hard metal or a cermet bodythat is uncoated or that is provided with a single- or multi-layercoating. The material selected for the cutting insert and for thecoating is largely a function of the material to be cut, which can be anon-ferrous metal, iron, or a casting material, e.g. a crankshaft.Moreover, the material selection is determined by the method parameters,where for milling crankshafts, which can be done both as inside millingand as outside milling, preferably high cutting speeds of more than 160m/min to 300 m/min are attained.

1. A cutting insert for clamping into a tool body shaped as a disk orbar, in particular for milling crankshafts, that is substantiallyparallelepipedal and has two front faces separated by a spacing defininga width of the cutting insert, two side faces that act as cuttingsurfaces separated by a spacing that determines a thickness of thecutting insert, and one upper and one lower end face, one concave [sic]edge surface being formed between each of the front faces and the upperside face or so the lower end face, such that the upper and lower endfaces and the convex edge surface each form with a side face a cuttingedge that ends laterally in cutting corners wherein an inwardly angledsurface abuts each of the convex edge surfaces and allows the respectivecutting corner to project, bevel faces angled to the outer edge areprovided between the inwardly angled surfaces on the front faces on bothsides of a planar support surface, and a width and a thickness of thecutting insert vary from each other by no more than 20%, and theypreferably are identical in length.
 2. The cutting insert in accordancewith claim 1 wherein a mounting bolt that in the clamped conditionpasses through a bore perpendicular to the front faces is shorter thanthe cutting edge length.
 3. The cutting insert in accordance with claim1 wherein between two chamfers the front face preferably has a flatsupport surface, the support surfaces of the two front faces beingexactly parallel to one another.
 4. The cutting inset in accordance withclaim 3 wherein a slope of the angled surface is 1° to 10° relative tothe respective support surface.
 5. The cutting insert in accordance withclaim 1 wherein the slope of the bevel face to the plane of the supportsurface is 15° to 30°.
 6. The cutting insert in accordance with claim 1wherein the support surfaces on a front face are flat surfaces thatflank the respective bore for receiving a mounting bolt and that arecoplanar with lines on and projecting past the respective convex edgesurfaces.
 7. The cutting insert in accordance with claim 1 wherein thecutting angle along the cutting edge is positive and at most 20°,preferably 10° to 15°.
 8. The cutting insert in accordance with claim 1wherein a chamfer preferably set at a chamfering angle of 0° to −15° isformed along the cutting edge.
 9. The cutting insert in accordance withclaim 1 wherein a radius of curvature for the convex edge surfaces is 1mm to 1.5 mm.